1. Field of the Invention
The present invention relates to quality of service (QoS) routers technology and, more particularly, to a QoS router system for effectively processing fragmented Internet Protocol (IP) packets and method thereof.
2. Description of Related Art
Conventionally, an IP fragmentation must be performed on a packet having a length larger than a maximum transmission unit (MTU) before the packet is sent to a specific interface via the IP layer. For example, as shown in FIG. 1A, a large packet is fragmented into three IP packets after the IP fragmentation is performed. Furthermore, as shown in FIG. 1B, each of the IP packets has the same identification (ID) and source IP address. This means that all three IP packets are formed from the same packet by means of IP fragmentation. Value ‘1’ in a more fragments (MF) bit of the ‘flag’ field means that there are subsequent IP packets originated from the same packet that has been fragmented by means of the same IP fragmentation. On the contrary, value ‘0’ in the MF bit of the ‘flag’ field means that there is no subsequent IP packet originated from the same packet which has been fragmented by means of the same IP fragmentation. Value in a field of fragment offset represents an offset of an IP packet within a packet that has not been fragmented by means of IP fragmentation. As shown, a first IP packet has a value of 0 in the field of fragment offset. Hence, a machine at a destination is able to reassemble the received IP packets.
A QoS router typically takes each packet as an independent one in deciding a passing or dropping of the packet without considering whether an IP fragmentation has been performed on the packet. Hence, the router may continuously allow subsequent fragmented IP packets to pass for being sent to a destination machine even a previous fragmented IP packet has been dropped when a plurality of fragmented IP packets originated from the same packet pass through the router. Unfortunately, in this case a complete original packet cannot be obtained at the destination machine by reassembling the passed fragmented IP packets because there is at least one fragmented IP packet dropped. This has the drawbacks of wasting channel bandwidth available on network and wasting both time and memory of the following routers and the destination machine for processing them. Therefore, it is desirable to provide a novel QoS router system and method for effectively processing fragmented IP packets for a potential reassembly of the same in order to mitigate and/or obviate the aforementioned problems.